A variety of imaging techniques are used for the medical diagnosis and treatment of patients. Ultrasound imaging represents a prevalent technique. Ultrasound uses sound waves to obtain a cross-sectional image of an object. These waves are radiated by a transducer, directed into the tissues of a patient, and reflected from the tissues. The transducer also operates as a receiver to receive the reflected waves and electronically process them for ultimate display.
Another imaging technique is referred to as Optical Coherence Tomography (OCT). OCT uses light to obtain a cross-sectional image of tissue. The use of light allows for faster scanning times than occurs in ultrasound technology. The depth of tissue scan in OCT is based on low coherence interferometry. Low coherence interferometry involves splitting a light beam from a low coherence light source into two beams, a sampling beam and a reference beam. These two beams are then used to form an interferometer. The sampling beam hits and penetrates the tissue, or other object, under measurement. The sampling or measurement beam is reflected or scattered from the tissue, carrying information about the reflecting points from the surface and the depth of tissue. The reference beam hits a reference reflector, such as, for example, a mirror or a diffraction grating, and reflects from the reference reflector. The reference reflector either moves or is designed such that the reflection occurs at different distances from the beam splitting point and returns at a different point in time or in space, which actually represents the depth of scan. The time for the reference beam to return represents the desirable depth of penetration of tissue by the sampling beam.
When the reflected beams meet, intensities from respective points with equal time delay form interference. A photodetector detects this interference and converts it into electrical signals. The signals are electronically processed and ultimately displayed, for example, on a computer screen or other monitor.
Optical coherence tomography (OCT) is a relatively new, non-invasive optical imaging technique. OCT is analogous in principle to pulse-echo ultrasound imaging, but near-infrared light waves instead of acoustic waves are employed to probe the sample specimen. OCT has been primarily applied to imaging of biological tissues, providing micron-scale resolution in three dimensions to a depth of a few millimeters without contacting the tissue. We here disclose a number of advanced designs and techniques that extend the utility of OCT and/or are based on OCT.
A number of papers and other references are cited below. These provide additional information and background concerning OCT, and they are incorporated by reference.
A number of features and embodiments are disclosed below; and it will be appreciated that the features may be combined and/or substituted for each other.